Hi all
i am now designing a box of silt overlaid by a layer of sand (as a mulch) of 2 cm thickness. Inside the box i put a cylinder of sand. However, when i tried to create mesh, i got this error "Surface boundary is not closed". I attached a snapshot of the problem and the file. Can anyone guide me on what shell i do. I tried to play with the boundary condition but i could not solve the problem.
I appreciate your helps

The error is described in the message box in your figure: Boundary of the solid is not closed on curve #25. You have to fix this topological error and make the boundary of Solid #2 closed/watertight. One of the necessary conditions is that each curve must have exactly two attached surfaces and these surfaces must be present in the list of boundary surfaces of the solid. For example, curve No. 7 in the attached figure has two connected surfaces: S2 and S5. In your case, curve #25 has just one attached surface (surface #11, while surface #25 (the pipe) is not part of the solid boundary) and therefore the boundary is not closed. You will either have to create intersection of surface #25 with surface #9 or replace surface #25 by two individual surfaces.